1. Field of the Invention
The present invention relates, in general, to technology applied to entertainment information devices, such as video game machines or computer game programs, information devices for representing geo-spatial information, or information devices for performing three-dimensional rendering using computer graphics and, more particularly, to a protruded displacement mapping method, which represents an object as protruding from a surface, and to a bi-layered displacement mapping method, which uses together such image-based protruded displacement mapping technology and typical shape-based displacement mapping technology in combination with each other.
2. Description of the Related Art
In the computer graphic fields, methods of representing the details of the surface of an object using the concepts of bump mapping, proposed by Blinn and disclosed in “Simulation of Wrinkled Surfaces” published in Proceedings of International Conference on Computer Graphics and Interactive Techniques, pp. 286-292, 1978, and displacement mapping, proposed by Cook and disclosed in “Shade Trees”, published in Proceedings of International Conference on Computer Graphics and Interactive Techniques, pp. 223-231, 1984, have been proposed.
The methods of representing the details of the surface of an object, proposed in the prior art, are classified into a triangle mesh generation method, based on shapes, and a displacement mapping method, based on images.
The triangle mesh generation method is a method of representing the details of the surface of an object by generating a large number of micro-polygons, and is problematic in that it is difficult to apply the triangle mesh generation method to an interactive program because a large number of micro-polygons is generated. In order to solve the problem, several methods of representing the displacement of the surface of an object without performing explicit rending using micro-polygons have been proposed. As the proposed methods, there are a ray tracing method, a three-dimensional reverse image warping method, a three-dimensional texture mapping method, a method of previously calculating visible information, etc. Of these methods, the ray tracing method and the reverse image warping method are not suitable for real-time applications because the amount of computational work is large. The three-dimensional texture mapping method is problematic in that, since polygons having two-dimensional textures are layered to perform displacement mapping, unnatural results may be obtained depending on the viewpoint. Further, the method of previously calculating visible information is problematic in that a large amount of memory must be used to store a sample for a five-dimensional function.
The image-based displacement mapping method is the method of representing the details of the surface of an object without generating micro-polygons, and uses a technique of simplifying or reproducing a ray-tracing method. However, such conventional methods all represent the detailed shape of the surface of an object using a method of depressing the bottom of the object downwards from a polygonal surface rather than protruding the object surface upwards from the polygonal surface.
FIG. 1 is a view showing the concept of a conventional image-based displacement mapping method. In FIG. 1, reference numeral 101 is an actual polygonal surface, reference numeral 102 is the depth from the actual polygonal surface to the object surface, reference numeral 103 is the height from a bottom surface to the object surface, and reference numeral 104 is a viewpoint.
In the prior art, in a virtual space implemented with the displacement map of an object, since the polygonal surface is placed uppermost, the height 103 actually represents the depth of the object, not the height of the object. The conventional methods are suitable for representing shapes depressed from the polygonal surface, which is a reference surface, but entail several problems when representing shapes protruding from the polygonal surface.
FIGS. 2A to 2D are views showing the problems of the conventional image-based displacement mapping method. In detail, FIG. 2A illustrates the rendering of a texture, in which a polygonal surface and a displacement map are not considered, FIGS. 2B and 2C illustrate the rendering of a texture, in which a polygonal surface and a displacement map are considered, and FIG. 2D illustrates the rendering of a texture, in which a polygonal surface and a displacement map are considered, and the processing of the surroundings thereof.
As shown in FIG. 2A, if a texture T, in which a polygonal surface P and a displacement map are not considered, is rendered, the height of an object is not considered in the rendered results.
If a displacement map is applied to the texture of FIG. 1A using the conventional image-based displacement mapping method, a bottom surface is depressed downwards, as shown in FIGS. 1B and 1C, and thus a region B, from which texture information is omitted, is generated near the boundary of the polygonal surface. When the height of the object is intended to be represented higher, the bottom surface of the object must be further depressed from the polygonal surface, so that the region B, from which information is omitted, is widened as the height of the object is increased (the information-omitted region of FIG. 1C is wider than that of FIG. 1B).
The problems of the conventional image-based displacement mapping method are summarized as follows. Since a bottom surface is depressed downwards from a polygonal surface without causing a texture to protrude upwards from the polygonal surface, the location of actual details varies due to the depression of the bottom surface. Further, as the bottom surface is depressed downwards, the bottom surface is moved further away from a person's viewpoint, so that a phenomenon in which the bottom surface is contracted occurs.
Because of the above problems, the conventional image-based displacement mapping method is problematic in that a bottom surface is depressed from a polygonal surface, the same file shapes are repeatedly arranged, as shown in FIG. 2D, and it is difficult to represent details of the surface of an object except for the case where the object is not high.